HONOLULU — The United States imposed fresh sanctions on North Korea on Friday, targeting the North’s defence industry and spy service in an attempt to punish Pyongyang for a crippling cyberattack against Sony. The sanctions marked the first public act of retribution by the U.S.

Although it was unclear how painful the blow would be — North Korea already is under tough U.S. sanctions — the move signalled that that the U.S. was not backing away from its insistence that North Korea is responsible for the attack against Sony. North Korea has denied involvement, and some cybersecurity experts say it’s possible the North wasn’t to blame.

“The order is not targeted at the people of North Korea, but rather is aimed at the government of North Korea and its activities that threaten the United States and others,” President Barack Obama wrote to a letter to House and Senate leaders.

None of the 10 individuals targeted by the U.S. are being sanctioned because they had any involvement in the cyberattack, Obama administration officials said. Rather, the U.S. sanctions were aimed at undermining North Korea’s defence sector, further isolating the government and creating a deterrent for future cyberattacks, said the officials, who briefed reporters on condition of anonymity.

The White House warned this was just the first part of the U.S. response to the Sony incident. Officials said more individuals will be sanctioned in the future.

North Koreans gather at the Mansu Hill where the statues of the late leaders Kim Il Sung, and Kim Jong Il tower over them, in Pyongyang, North Korea. (AP Photo/Wong Maye-E, File)

The stepped-up sanctions, authorized by Obama, will also affect three North Korean entities that are already subject to U.S. sanctions. The U.S. has extensive sanctions in place against North Korea over its nuclear program, but these are the first sanctions punishing Pyongyang for alleged cyberattacks.

The FBI has blamed North Korea for the crippling cyberattack against Sony Pictures Entertainment. North Korea has denied involvement but has expressed fury over a comedy film by Sony that mocked North Korea’s leader. Sony Pictures initially called off release of the film, citing threats of terror attacks against U.S. movie theatres. Obama criticized Sony’s decision, and the movie opened last month.

A nearly 10-hour shutdown of North Korean websites last week prompted widespread speculation that the U.S. had launched a counterattack in retribution, but the White House did not comment on whether the U.S. was responsible. The U.S. has vowed a proportional response to the Sony incident but has warned its response would “take place at a time and in a manner of our choosing.”

North Korea and the U.S. remain technically in a state of war because the 1950-53 Korean War ended with an armistice, not a peace treaty. The rivals also are locked in an international standoff over North Korea’s nuclear and missile programs and its alleged human rights abuses.

Among those sanctioned Friday are organizations tied closely to North Korea’s defence industry:

–Korea Mining Development Trading Corporation, the state-owned arms dealer and exporter of equipment related to ballistic missiles and conventional weapons.

–Korea Tangun Trading Corporation, which obtains technology to support North Korea’s defence research.